Issue |
A&A
Volume 526, February 2011
|
|
---|---|---|
Article Number | A20 | |
Number of page(s) | 13 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361/201014617 | |
Published online | 15 December 2010 |
Equatorial coronal holes, solar wind high-speed streams, and their geoeffectiveness⋆
1
Department of GeophysicsFaculty of Science, University of
Zagreb, Horvatovac
95, 10000
Zagreb, Croatia
e-mail: verbanac@irb.hr
2
Hvar Observatory, Faculty of Geodesy, University of
Zagreb, Kačićeva
26, 10000
Zagreb,
Croatia
3
Institute for Physics, University of Graz, Universitätsplatz
5, 8010
Graz,
Austria
Received: 31 March 2010
Accepted: 9 October 2010
Context. Solar wind high-speed streams (HSSs), originating in equatorial coronal holes (CHs), are the main driver of the geomagnetic activity in the late-declining phase of the solar cycle.
Aims. We analyze correlations between CH characteristics, HSSs parameters, and the geomagnetic activity indices, to establish empirical relationships that would provide forecasting of the solar wind characteristics, as well as the effect of HSSs on the geomagnetic activity in periods when the effect of coronal mass ejections is low.
Methods. We apply the cross-correlation analysis to the fractional CH area (CH) measured between central meridian distances ± 10°, solar wind parameters (flow velocity V, proton density n, temperature T, and the magnetic field B), and the geomagnetic indices Dst and Ap.
Results. The cross-correlation analysis reveals a high degree of correlation between all studied parameters. In particular, we show that the Ap index is considerably more sensitive to HSS and CH characteristics than Dst. The Ap and Dst indices are most tightly correlated with the solar wind parameter BV2.
Conclusions. From the point of view of space weather, the most important result is that the established empirical relationships provide a few-days-in-advance forecasting of the HSS characteristics and the related geomagnetic activity at the six-hour resolution.
Key words: Sun: corona / solar-terrestrial relations / solar wind
Appendices, Figs. 9–14, and table 4 are only available in electronic form at http://www.aanda.org
© ESO, 2010
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